A conventional multiple-cylinder internal combustion engine feeds fresh air to each cylinder through a carburetor by means of mechanism which provides connection of tip portions of a plurality of branched air intake tubes to an air-intake hole of each cylinder, and also connection of the carburetor to an inlet in the center of the assembly of air-intake tubes. A conventional carburetor is provided with primary and secondary barrels. Of these, the secondary barrel opens as soon as the vehicle reaches a certain speed faster than medium speed. As shown in FIG. 5, the conventional primary and secondary barrels are respectively provided with a small venturi B inwardly above a large venturi A. Fuel nozzle C opens into the venturi B, and its fuel supply tube D, by which it is connected to the float chamber E, extends radially partially across the large venturi A. As a result, air resistance increases in such region where the fuel tube D traverses, thus causing air-flow velocity V2 downstream thereof to be slower than air-flow velocity V1 which is present in such region where the fuel tube D does not traverse. This is turn causes more volume of fuel to flow through the portion of the carburetor barrel where air-flow velocity V1 is present, and thus resulting in an increased rate of fuel against air in the barrel portion where V1 is present. Even though the carburetor is mounted by an assembly unit provided at the center of a plurality of branched air-intake tubes, the ratio of fuel inside the cylinders supplied by V1 increases to eventually generate uneven fuel concentration between cylinders. This adversely affects the startup performance, driving comfortability without knocking, exhaust-gas control characteristic, and power-output characteristic of the vehicle itself.
To prevent those adverse effects mentioned above, Japanese Utility Model Publication No. 56-24305 (1981) and Japanese Utility Model Laid-Open No. 55-23458 (1980) have proposed use of modified multiple air-intake tubes. However, both of these systems require complex constitution of multiple air-intake tubes, and both require a variety of casting processes.
The primary objection of the invention is to provide a novel air distribution apparatus for use with an internal combustion engine, which securely generates exceeding performance of the engine by easily and properly balancing the ratio of air against fuel in the air-intake port of every cylinder by effectively displacing the position of carburetor connection to the assembly of multiple air-intake tubes.